.hi-boot abuse

[Simon Marlow]

> I have a question which came up as a result of some attempts 
> to enforce
> seperate compilation. Suppose we have two modules as follows:
> 
> ------ A.hs --------
> module A (AbstractType) where
> 
> data AbstractType = it's hidden implementation
> 
> f :: AbstractType -> String
> f _ = "foo"
> 
> g :: AbstractType
> g = something
> 
> ------ B.hs ---------
> module B where
> import A
> 
> s = f g
> 
> 
> Now, I want to be able to Compile A, Compile B, change the
> implementation of AbstractType in A, recompile A, and then not have to
> recompile B. Unfortunately, this doesn't seem to happen in 
> GHC 6.0.1, as
> the representation of AbstractType is placed in A.hi, so when the
> representation changes, it forces a recompilation of B.

Good point.  Following some changes made by Simon P.J. recently, GHC
will in the future not put the representation of an abstract type in the
interface file when not optimising.  This change will appear in 6.4.

Your .hi-boot trick looks like it *might* be ok, but no guarantees!

Cheers,
	Simon